This invention relates to manholes of the type used to protect and limit access to underground chambers or vaults and more particularly relates to a bracket that provides a prosthetic repair appliance that allows a considerably quicker, easier and less expensive repair of a manhole base with a broken cover anchoring tab by providing a substitute for the broken anchoring tab.
Manholes are commonly found in many places and are known by a variety of names including maintenance hole and access hole. A manhole is the top, usually vertical and cylindrical passage to an underground chamber or vault. The chamber or vault houses an access point for making connections, performing maintenance or accessing an underground material or device for measurement purposes.
Referring to FIGS. 1-4, typically the top opening into the manhole is surrounded by a base 10 with a central opening 12 and an outwardly extending flange 14. The base 10 supports a cover 16 for inhibiting unauthorized access and/or preventing entry of surface liquids and other surface materials into the manhole. The manhole cover 16 is supported on the base 10 usually on a mating surrounding recessed ledge 18 that is formed to receive the cover 16 so that the top of the cover 16 is in the same horizontal plane as the top of the base 10 and the cover 16 is confined against lateral horizontal movement on the base 10. The base 10 and cover 16 are usually made of cast iron but some are made of precast concrete, glass reinforced plastic or other materials. The base 10 and its cover 16 are often installed over a manhole in a paved area so that the top of the base flange 14 and the top of the cover 16 are level with the surface of the pavement or surrounding grout.
Around the inner wall 20 of the base 10 there is usually a lip, flange or shoulder (herein referred to as a lip 22) which protrudes inwardly and surrounds the inner wall 20 of the base 10 and is in a plane parallel to the top surface of the base. Most commonly, the upper (in the installed orientation) surface of the lip 22 is offset below the top of the base to form the recessed ledge 18 that supports the cover 16. However, the lip 22 can be formed separately and independently of the recessed ledge 18 and, although not preferred, an embodiment of the invention can be used even in the absence of a lip. The underside of the lip 22 has a downward facing surface 24 which is important because that surface 24 can engage preferred embodiments of the invention for reasons that subsequently will be described.
Most manholes are cylindrical with a circular base and cover for a variety of reasons including that the circular shape prevents the manhole cover from falling into the manhole. However, there are also square and rectangular manholes, with correspondingly shaped bases, covers and lips. The invention is also applicable to those manholes as well as manholes of other shapes.
A manhole base 10 typically has anchoring tabs 26 for attachment of the manhole cover 16 to the base 10 by means of threaded bolts 28. The tabs 26 are usually cast integrally with the base 10 and protrude inwardly from the inner wall 20 of the base 10 and often from the lip 22. For circular manhole bases there most commonly are two diametrically opposite tabs although there can also be three or more tabs spaced around a circular inner wall. For square, rectangular or triangular manhole bases there may be a tab on each side or just on two sides. The anchoring tabs 26 have tapped holes 30 so they have female threads to permit the cover 16 to be attached to the base 10 with the threaded bolts 28. The threaded bolts 28 extend through countersunk holes in the cover 16 and into the tapped holes 30 to bolt down the cover 16 onto the base 10.
Referring to FIG. 4, an example of a manhole for which the invention is well suited is a manhole that houses a well 32 of smaller exterior diameter than the inner diameter of the base 10. The top end of the well 32 terminates below the level of the base and the bottom end of the well 32 terminates in an underground earth-walled chamber. Wells of this type are used for sampling ground water such as in the soil beneath or adjacent underground fuel tanks that are buried below the pavement at gas stations. However, the invention is suitable for use on other manholes such as common street manholes for accessing sewers and utility underground passageways.
Manholes of various types also usually have a casing or sleeve 34 of material to prevent the surrounding earth from eroding into the manhole. For example, a manhole of the type described above has a cylindrical metal sleeve 34 that seats against a cylindrical surface of the manhole base 10.
There is, however, a problem with manhole bases and the invention greatly alleviates that problem. The materials from which manhole bases are fabricated, such as cast iron, are relatively brittle and break under tension forces, especially at very low temperatures. Consequently, the cover anchoring tabs often break off from the base. For example, dirt or sand can support parts of the cover above the recessed ledge and act as a fulcrum. An automobile tire running over an unsupported part of the cover can cause the cover to act as a lever that applies an excessive upward force through a cover bolt to its tab. Another cause of tab breakage is snow plow blades striking the cover.
If both tabs become broken, the cover is no longer secured to the base and therefore is more easily removed, such as by vandalism, which permits unauthorized access and the entry of surface contaminants. If only one of the tabs is broken, the cover becomes loose and noisily tilts when driven over by a vehicle tire.
The current manner of repairing the broken cover anchoring tabs is to replace the entire base. Base replacement requires a repair crew to dig up the concrete or grout that immediately surrounds the base, lift out the base and replace it with a new base. Then new concrete or grout must be poured around the base and permitted to harden. This repair requires not only the purchase of a new base but also several man-hours to complete. A repair of this type additionally requires a time delay after the repair is completed and during which time the manhole site must be blocked from vehicle traffic while the concrete or grout hardens.
It is therefore an object and feature of the invention to provide a prosthetic repair appliance that is less costly than a new manhole base, requires far fewer man-hours for completion of a repair, and allows the manhole to be returned to normal use immediately after the repair is completed.